1. Field of the Invention
The present invention relates to an x-ray collimator for use in an electron beam computed tomography scanner, and more particularly, to an x-ray collimator formed using a fixed position x-ray blocking septum having an aperture therein. In a preferred embodiment a movable ring is also provided having a longitudinal axis positioned coaxially with the aperture in the septum.
2. Description of the Prior Art
In computed tomography (CT) scanners having a scanning electron beam x-ray source, an electron beam is magnetically deflected so as to rotate in a generally circular path, and in doing so, impinge upon a ring-shaped target, thereby generating a rotating source of x-rays. After passing through a collimator, the x-rays are shaped into a fan beam and then intercepted by a ring-shaped detector array which overlaps the collimator. U.S. Pat. No. 4,352,021 issued Sep. 28, 1982 discloses such an electron beam scanner, which scanners are commercially available, e.g., from Imatron, Inc., located in South San Francisco, Calif. In order to collimate the x-rays emitted from a ring-shaped target, prior art collimators have been formed by fixing on a plastic cylinder first and second metallic rings having a defined space therebetween, which space establishes the x-ray fan beam and defines a given slice width. In order to change the slice width, a second set of metallic rings having a different defined space therebetween are provided on another portion of the plastic cylinder, which is spaced away from the first set. The second set effectively comprises a new collimator which must be mechanically substituted for the first collimator. The substitution is accomplished by positioning the second set of rings over the target in order to establish the new collimator.
The forenoted prior art collimator arrangement is relatively expensive due to the mechanical construction of multiple sets of collimators and the mechanical adjusting arrangements which are necessary in order to accurately position the appropriate set of collimator rings with respect to the target ring and the detector array. Additionally, the slice (or x-ray fan beam) width is fixed by the position established between the different sets of collimator rings and is therefore not continuously variable.
It would be desirable to provide a lower-cost collimator assembly useful for electron beam (EB) computed tomography (CT) scanners.
It would be even more desirable to provide such a lower-cost collimator which would provide improved performance.